1. Field of the Invention
The present invention relates generally to a motor rotor, and more particularly to a motor rotor and rotating shaft thereof having engagement structure for fixing magnetic bodies to the rotating shaft.
2. Description of Related Art
A motor (electromotor) is used to convert electrical energy into mechanical energy so as to provide rotary motion. Besides directly providing rotary motion, the motor also can convert rotary mechanical energy into linear motion or vibrating motion by combining with different mechanisms.
A motor for providing rotary motion comprises a stator and a rotor, wherein the stator is the stationary part of the motor, which provides a magnetic field; the rotor is the rotary part of the motor, which rotates according to the magnetic field. The rotor generally comprises a rotating shaft formed by stacking a plurality of silicon steel sheets and a plurality of permanent magnets spacedly adhered to an outer circumferential surface of the rotating shaft. As the permanent magnets are fixed to the rotating shaft by adhering, the permanent magnets can easily be adversely affected by external environment factors and detached from the rotating shaft, thus inevitably disturbing normal operation of the motor rotor and even causing the rotor to be stuck in the stator.
The above-described environment factors can be, but not limited to, temperature and humidity. If the surrounding temperature around the motor greatly changes (for example, the motor operates in a cold area below zero degree), delamination can occur due to different thermal expansion coefficients between the permanent magnets and the silicon steel sheets. On the other hand, if the humidity around the motor greatly changes (for example, the motor operates in a humid area or in water), the silicon steel sheets gradually gather rust and the rust further presses the adhesive layer (the cured adhesive), thereby causing delamination to occur. Therefore, the above-describe environment factors directly shorten the lifetime of the motor. How to prevent the environment factors from adversely affecting the lifetime of the motor has become important.
In order to overcome the above-described lifetime shortening problem caused by the adhering method, engagement structures for assembling the permanent magnets to the rotating shaft are proposed. Typically, a plurality of engagement grooves spaced apart with an equal interval is disposed on an outer circumferential surface of the rotating shaft for engaging with the permanent magnets, wherein clearance generated during assembly is helpful to overcome delamination caused by environment factors. However, as the silicon steel sheets and the permanent magnets are fabricated by different techniques having different precisions, great variation can occur during assembly engagement, which often leads to cracking of the crisp permanent magnets when the magnets are engaged with the engagement grooves, thus seriously affecting the assembly yield.
FIG. 1 is a structural diagram of a motor rotor 1 disclosed by Taiwan Patent No. 412,100. As shown in FIG. 1, the motor rotor 1 comprises a plurality of silicon steel sheets 11, a plurality of permanent magnets 13, a plurality of bolts 15, and two end covering plates 17. The plurality of silicon steel sheets 11 is stacked so as to form a rotating shaft. A plurality of fixing grooves 111 is formed along an outer circumferential surface of each silicon steel sheet 11 and spaced apart with an equal interval such that the bolts 15 can be inserted and fixed therein, thereby fixing the plurality of permanent magnets 13 to the outer circumferential surface of the rotating shaft. That is, the permanent magnets 13 are each embedded between two adjacent bolts 15. The end covering plates 17 disposed at two ends of the rotating shaft are used to fix the permanent magnets 13 and the bolts 15 to the rotating shaft and prevent them from detaching from the two ends of the rotating shaft.
As the above-described invention uses additional elements such as the bolts 15 and the two end covering plates 17, the element cost, the assembly cost and the warehousing cost are increased. Further, because the punching precision of the grooves 111 and the machining precision of the permanent magnets 13 have a difference of at least onefold, the assembly precision is not easy to control. Accordingly, the grooves and the permanent magnets can have clearance fit or interference fit. If the interference fit appears, when the bolts 15 are inserted to the fixing grooves, the bolts 15 can press the permanent magnets 13 so as to cause the permanent magnets 13 to crack, thereby significantly affecting the fabrication yield and greatly increasing the fabrication cost.
FIG. 2 is structural diagram of a motor rotor 2 disclosed by Taiwan Patent No. 595072. As shown in FIG. 2, the motor rotor 2 comprises a rotating shaft 21, a plurality of permanent magnets 23 and embedding teeth 25. The rotating shaft 21 is integrally formed by silicon steel and a plurality of embedding bumps 211 is spacedly formed along an outer circumferential surface of the rotating shaft 21. Each permanent magnet 23 is disposed to the outer circumferential surface of the rotating shaft 21 at a position between two adjacent embedding bumps 211, and the embedding teeth 25, each of which has grooves corresponding to the embedding bump 211, are engaged with the embedding bumps 211 such that the permanent magnets 23 can be fixed by adjacent embedding teeth 25.
However, as the above-described teeth 25 should be fabricated according to the shape and size of the permanent magnets 23 and the grooves of the embedding teeth 25 should be fabricated according to the shape and size of the embedding bumps 211, the requirement on fabrication precision is high. Also, the large number of the embedding teeth 25 leads to high element cost, high assembly cost and high warehousing cost. In addition, as the embedding teeth 25 and the permanent magnets 23 must be closely attached with each other so as to ensure a wanted fixing effect, the fabrication error can form a continuous accumulating error, which can easily cause vibration and loosening of the permanent magnets 23, especially when affected by the above-described environment factors.
Therefore, there is a need to provide a rotating shaft and a motor rotor having the same so as to overcome the above-described drawbacks.